On Thu, 01 Feb 2007 12:58:14 GMT, "colin"
wrote:

well normally in order to cuase an explosion you have to have a combustable
material that burns very quickly,
the force comes from the fact that the burnt material wich is oxidesed takes
up a great deal more volume
and until it expands is under great pressure. in an empty oven there is no
combustables.


WEll, almost right... (and your 'normally' does apply, so what you say
is true, but there's more! bg)

All you need is pressure, not a combustable substance.

In the case of the balls that 'exploded' were they to have a 'strong'
outter shell, and a high moisture content inside, the moisture could
easily convert to steam and build up pressure until the outer shell
failed--an explosion... It would not be difficult to build up a
hundred PSI of steam pressure, and that would result in a rather large
'bang'!